1. Field of the Invention
This invention relates to a radio telephone apparatus for transmitting and receiving voice information signals as electrical waves. More particularly, it relates to a portable radio telephone apparatus having enclosed therein a power source for supplying a driving power to a receiver section provided with a speaker unit and to a transmitter section provided with a microphone unit.
2. Description of the Prior Art
Up to now, there is proposed a radio telephone apparatus adapted to transmit information signals entered as acoustic signals to a telephone exchange station as electrical waves and to receive the information signals transmitted as electrical waves from the telephone exchange station to output the received signals as acoustic signals.
Such a radio telephone apparatus includes a receiver section provided with a speaker unit for converting electrical waves into acoustic signals and a transmitter section provided with a microphone unit for converting the acoustic signals into electrical signals. The radio telephone apparatus also includes a transmitting section for transmitting the electrical signals sent from the transmitter section as electrical waves and a receiving section for receiving electrical waves and transmitting the received electrical waves to the receiver section as electrical signals. The receiver section, transmitter section, transmitting section and the receiving section are provided as electronic circuits each constructed or predetermined electronic components.
Such a radio telephone apparatus which is reduced in size so as to be portable is shown in FIG. 1 and formed of the receiver section, transmitter section, transmitting section and the receiving section, all of which are enclosed in a unitary casing 101. This casing 101 has the speaker unit 102 and the microphone unit 103 enclosed within upper and lower end portions in the drawing, respectively. The casing 101 is bent slightly in contour so as to lie along the user's face with the speaker unit 102 facing to the user's auricle and with the microphone unit-103 facing to the user's mouth.
The radio telephone apparatus is also provided with a power source casing 105 containing a power source device 104, such as a dry cell or a chargeable battery, for supplying the driving power to the receiver section, transmitter section, transmitting section and to receiving section. This power source casing 105 is removably attached to the back side of the casing 101 opposite to the side thereof confronting to the face of the user of the radio telephone apparatus.
A ringer device 106 is provided within the casing 101. The ringer device 106 is constructed for issuing an acoustic sound for giving notice that the electrical waves sent from the telephone exchange station have been received by the receiver section or confirming the user's operation on the transmitter section. This acoustic sound may, for example, be of a constant unitary frequency and interrupted at a predetermined interval on the order of a few seconds.
With the above described radio telephone apparatus, the total usable time by a given power source device is determined by the storage capacity of the power source device. Thus, with the above described radio telephone apparatus, if the time during which the apparatus may be used by one charging operation of a sole power device is set to be longer, the power source device is bulky and can hardly be reduced in size.
If a small-sized power source device with a small storage capacity is used for reducing the size of the radio telephone apparatus, the usable time of the apparatus is shortened and hence the apparatus may become unusuable while it is in use. That is, if the power supply becomes low during usage, transmission and reception of the electrical waves become unfeasible and hence the talk over the telephone may be terminated.
On the other hand, since the ringer device 106 is provided in the casing 101, the acoustic sound produced by the ringer device 106 is propagated through the casing 101 so as to be allowed out by way of a through-hole by which the speaker unit 102 faces the outside of the outer casing 101. The ringer device is adapted to emit an acoustic sound of a sound pressure which may be felt by the user at a distance of, for example, one to two meters from the radio telephone apparatus.
Thus, when the ringer device is actuated while the radio telephone apparatus is in use with the speaker unit 102 lying in close proximity to the user's auricle, there is the risk that the sound emitted by the ringer device will reach the user's auditory meatus with an excessive sound pressure. If the acoustic sound with an excessive sound pressure reaches the user's auditory meatus, not only may the user feel uncomfortable, but the user's tympanic membrane may be damaged.